Submitted to: Journal of Evolutionary Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2004
Publication Date: 2/23/2005
Citation: Copeland, C.S., Mann, V.H., Morales, M.E., Kalinna, B.H., Brindley, P.J. 2005. The Sinbad retrotransposon from the genome of the human blood fluke, Schistosoma mansoni, and the distribution of related Pao-like elements. Journal of Evolutionary Biology. 5(1):20. Interpretive Summary: Schistosoma mansoni, the African blood fluke, causes schistosomiasis, a serious parasitic disease second only to malaria in terms of morbidity. This parasitic worm is widespread in Africa and Latin America, and infects humans by directly penetrating skin from contaminated water, making public health based control of the disease difficult. (Unlike ingested parasites, since these worms penetrate skin, filtering or boiling drinking water will not solve the problem.) A vaccine would be the perfect solution, but no vaccine is currently available. One of the reasons a vaccine has not been developed is that the schistosome genome is not understood well enough to take full advantage of the powerful molecular tools available for many other diseases. While at Tulane University a scientist now at the Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) enhanced the understanding of the genome of Schistosoma mansoni. At least half of the schistosome genome is thought to be made up of mobile genetic elements, including retrotransposons. Retrotransposons are semi-autonomous stretches of DNA copy themselves into new locations in the genome, and are similar to retroviruses like HIV. Sinbad, is a new Pao-like retrotransposon was discovered in the genome of Schistosoma mansoni. As more such information accumulates the chances of vaccine development will increase.
Technical Abstract: Of the major families of long terminal repeat (LTR) retrotransposons, the Pao/BEL family is probably the least well studied. It is becoming apparent that numerous LTR retrotransposons and other mobile genetic elements have colonized the genome of the human blood fluke, Schistosoma mansoni. A proviral form of Sinbad, a new LTR retrotransposon, was identified in the genome of S. mansoni. Phylogenetic analysis indicated that Sinbad belongs to one of five discreet subfamilies of Pao/BEL like elements. BLAST searches of whole genomes and EST databases indicated that members of this clade occurred in species of the Insecta, Nematoda, Echinodermata and Chordata, as well as Platyhelminthes, but were absent from all plants, fungi and lower eukaryotes examined. Among the deuterostomes examined, only aquatic species harbored these types of elements. All four species of nematode examined were positive for Sinbad sequences, although among insect and vertebrate genomes, some were positive and some negative. The full length, consensus Sinbad retrotransposon was 6,287 bp long and was flanked at its 5'- and 3'-ends by identical LTRs of 386 bp. Sinbad displayed a triple Cys-His RNA binding motif characteristic of Gag of Pao/BEL-like elements, followed by the enzymatic domains of protease, reverse transcriptase (RT), RNAseH, and integrase, in that order. A phylogenetic tree of deduced RT sequences from 26 elements revealed that Sinbad was most closely related to an unnamed element from the zebrafish Danio rerio and to Saci-1, also from S. mansoni. It was also closely related to Pao from Bombyx mori and to Ninja of Drosophila simulans. Sinbad was only distantly related to the other schistosome LTR retrotransposons Boudicca, Gulliver, Saci-2, Saci-3, and Fugitive, which are gypsy-like. Southern hybridization and bioinformatics analyses indicated that there were about 50 copies of Sinbad in the S. mansoni genome. The presence of ESTs representing transcripts of Sinbad in numerous developmental stages of S. mansoni along with the identical 5'- and 3'-LTR sequences suggests that Sinbad is an active retrotransposon. Sinbad is a Pao/BEL type retrotransposon from the genome of S. mansoni. The Pao/BEL group appears to be comprised of at least five discrete subfamilies, which tend to cluster with host species phylogeny. Pao/BEL type elements appear to have colonized only the genomes of the Animalia. The distribution of these elements in the Ecdysozoa, Deuterostomia, and Lophotrochozoa is discontinuous, suggesting horizontal transmission and/or efficient elimination of Pao-like mobile genetic elements from some genomes.